And call function notify on the channel (from server side)
when you want to notify the client.

To get back the notify functions for one user, you may want to
iterate on all client process states.
To do that, create a session group for each user
(see How to save session data).
Here we suppose that the session group name is the user_id, as a string.
Then iterate on all sessions from this group, and on all client processes
for each session.

For example:

letnotifyuser_idv=(* We get the session group state for this user: *)letstate=Eliom_state.Ext.volatile_data_group_state~scope:Eliom_common.default_group_scope(Int64.to_stringuser_id)in(* We iterate on all sessions from the group: *)Eliom_state.Ext.iter_volatile_sub_states~state(funstate->(* We iterate on all client process states in the session: *)Eliom_state.Ext.iter_volatile_sub_states~state(funstate->let(_,notify)=Eliom_reference.Volatile.Ext.getstatechannel_refinnotify(Somev)))

Warning: If you do not call the iterators during
a request or during the initialisation phase of the Eliom module,
you must provide the extra parameter ?sitedata,
that you can get by calling Eliom_request_info.get_sitedata
during the initialisation phase of the Eliom module.